I don't think you could hold etymological data as a historical inaccuracy. Based on the Crusades, the movie was taking place around the eleventh century. The English language as we know it today is has only been around since the sixteenth century. Since it would be ridiculous for an audience to sit through a movie spoken entirely in Middle English, the movie is done almost entirely using words not yet in use.

While Maid Marian was in the woods she says "Men speak of love easily when it suits their purpose" this is a line from Shakespeare "As you like it" in this play a charcter in the 2nd scene says "the count is in the forest of Arden like Robin hood and his merry men" Which one came 1st??

Hollywood movies = art sometimes more important than truth.
A real slip-up was Costner landing near the white cliffs of Dover and taking in a fighting break at Hadrian's Wall before reaching Nottinghamshire later the same day. I defy anyone on land-based transport to drive from Sussex to Northumbria and back to Mansfield in such a short time - check it on a map. Didn't bother me though, I expect it from Hollywood. More entertainment than truth, so this slip-up is bogus. Just suspend your disbelief.